Voltage regulator

ABSTRACT

Voltage regulators designed for connection in series with an alternating current source and a load and employing a three-leg, two-window transformer are disclosed. Secondary windings on the two outer transformer core legs are interconnected to form a pair of secondary winding systems and the systems are interconnected via a variable resistance. Voltage regulation is achieved by varying the flux distribution in the transformer core by employing variable resistance to distribute the load current between the winding systems.

United States Patent [72] lnventor Sherwood Thaler Lexington, Mass. [21] Appl. No. 865,811 [22] Filed Oct. 13, 1969 [45] Patented Mar. 23,1971 [73] A i The United States of America as represented by the Administrator of the National Aeronautics and Space Administration 1 YQL AQE REGULAIQ 3 Claims, 5 Drawing Figs.

[52] US. Cl 323/48, I 313/60 [51] Int. Cl H0lf 19/00, 1-10lf29/00 [50] Field ofSearch 323/48,49, 57, 60, 61, 83, 87, 88; 321/57, 68; 336/155, 170, 180, 182, 214

[56] References Cited UNITED STATES PATENTS 2,603,771 7/1952 Walsh 323/60X 2,686,291 8/1954 Macklem 321/57X 2,999,973 9/1961 Medlar..... 323/60 3,447,068 5/1969 Hart 323/60 FOREIGN PATENTS 869,841 6/1961 Great Britain 323/60 Primary Examiner- Gerald Goldberg Attorneys-Marvin J. Marnack, Marvin F. Matthews and John R. Manning ABSTRACT: Voltage regulators designed for connection in series with an alternating current source and a load and employing a three-leg, two-window transformer are disclosed.

Secondary windings on the two outer transformer core legs are interconnected to form a pair of secondary winding systems and the systems are interconnected via a variable resistance. Voltage regulation is achieved by varying the flux distribution in the transformer core by employing variable resistance to distribute the load current between the winding systems.

PATENTED MAR23 |97l FIC-ll CONTROL CIRCUITRY O 2 ptw E;

CONTROL CIRCUITRY 42 ".FIG.4

E F] 3 AVERAGE m .A R D P INVENTOR SHERWOOD THALER MIN. MAX. E in (VOLTS) T QLTAQEREGTJLALLQR ORlGlN OF THE lNVENTION The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTEON 1. Field of the invention The present invention relates to the regulation of the voltage applied to a load from an unregulated voltage source. More specifically, the present invention is directed to voltage regulator apparatus intended for connection in series with a source of alternating current and a load. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.

2. Description of the Prior Art Series regulators which may be connected between an unregulated, varying voltage source and a load and which will cause application of a constant output voltage to the load are well-known in the art. The typical prior art series regulator is a relatively inefficient device in that, in order to obtain output voltage regulation, it depends upon the steady-state dissipation of substantial amounts of power in an element connected in series with the load. Further, in prior art series regulators the power dissipated in the series element will vary directly with the source voltage. Accordingly, the power dissipation element must be sized so that it will dissipate the requisite power with the maximum expected input voltage without overheating and the element must also be able to dissipate a fair amount of power over long periods since it normally operates approximately midrange of the expected input voltage excursions. These design criteria, of course, add size and weight to the voltage regulator while calling for the wasteful dissipation of substantial amounts of power in the series connected element.

Also known in the art are switching-type series regulators which achieve a constant output voltage level by means of varying the duty cycle of switching elements connected between the source and load. Thus, through the use of suitable logic circuitry which senses the load voltage level, the series connected switching element may be caused to conduct or interrupt the power flow thereby coupling the source to the load theoretically with infinite or zero attenuation. As is well known, prior art switching regulators of the on-off type are characterized by an output with very high ripple and substantial switching transients superimposed thereon. While the ripple and transients can be removed from the output voltage by filtering, the weight and expense of the requisite filters prohibits the use of the switching regulator in many applications. Also, prior art switching regulators have the disadvantage of drawing discontinuous current from the source thereby requiring an input filter or other penalizing factors in the system configuration.

SUMMARY OF THE INVENTlON The present invention overcomes the foregoing and other disadvantages of the prior art by providing a novel series regulator which maintains, from an unregulated and varying input voltage, a constant output potential. The regulator of the present invention employs a novel transformer and circuit configuration which couples the unregulated source to a load in such a manner that the power dissipated in the regulator is at a minimum at both extremes of the normally expected source output voltage magnitude range. in accomplishing the foregoing, the present invention employs a transformer structure of the three-leg, two-window type. A primary winding connected to the voltage source is wound on the center leg of the transformer core and a plurality of secondary windings are wound on the outer core legs. Through the use of control circuitry and either a switch or series connected variable resistance, the flux distribution through the outer legs of the transformer core is controlled thereby controlling the voltage induced in the several secondary windings. Accordingly, by properly interconnecting the transformer secondary windings, the power coupled from the source to the load may be modulated, by varying the flux distribution in the transformer core to thereby add a variable amount of power to the minimum amount constantly being transmitted to the load, and the output voltage maintained at a preselected level.

BRIEF DESCRIPTION UP THE DRAWING The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the various figures and in which:

FIG. l is a schematic view of a transformer for use in the present invention;

FIG. 2 is a schematic showing of a first embodiment of a voltage regulator in accordance with the present invention;

FIG. 3 is a graph which depicts the power savings realized through use of the present invention;

FIG. 4 is a schematic showing of a second embodiment of a voltage regulator in accordance with the present invention; and

FIG. 5 is a waveform diagram depicting the unfiltered output voltage obtained from the embodiment of FIG. 4 under the condition of nominal input voltage.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to FIG. 1, a three-leg transformer core is indicated at 10. The core 10 has, wound on the center leg thereof, a primary winding 12. A first of the outer legs of the transformer core has a single, center-tapped secondary winding 14 wound thereon. The other outer transformer core leg has three separate secondary windings wound thereon. These secondary windings are respectively indicated at 16, lb and 20. The winding 20 is center tapped.

The manner of interconnection of the secondary windings wound on the transformer core It) and the operation of the present invention may be understood from a consideration of FIG. 2. The secondary winding 2i), which comprises a first secondary winding system will have its center tap directly connected to one side of a load while the opposite ends of the winding 20 will be connected, via a pair of similarly poled diodes 22; and 24, to the other side of the load. The secondary windings l6 and lb are connected to respective ends of the center-tapped secondary winding M and the other ends of windings l6 and iii are coupled, via a pair of respective, similarly poled diodes 2d and 2b, to the input of a series regulator, indicated generally at Bil. The center tap of the secondary winding 14 is connected to the same side of the load as the center tap of secondary winding 24). The interconnected windings l4, l6 and 18 form the second secondary winding system.

The series regulator 36 comprises a variable resistance element 32 connected between the series connected secondary windings id, lid and iii and load. The series regulator M will also comprise control circuitry 34, which is state-of-the-art and does not comprise part of the present invention, which varies the resistance of element 32, in a manner well-known in the art, in accordance with sensed variations in the line voltage applied to the transformer primary winding E2. The control circuitry 34 may, for example, comprise a differential amplifier which senses discrepancies between the actual output voltage and a reference source. Error signals from the differential amplifier may be employed, in a known manner, to cause the resistance of power handling element 32 to vary so as to achieve the desired output voltage. While element 32 has been shown as a variable resistor, it is to be understood that the power handling element will actually comprise a transistor or FET. in the case of the embodiment of PEG. 4, the output of the differential amplifier would be used to vary the duration of the open and closed periods of switch 4t). Control systems of the type which can be used with the present invention are described in general in Chapter 8 of the Handbook of Selected Semiconductor Circuits," US. Government Printing Office publication No. NObsr 73231, NAVSl-llPS 93484, 1960. Control circuits particularly suited for use with the embodimentof F110. 2 of the present invention are discussed at pages 8-16 through 8-19, 8-38 and 8-41 of the Handboolr" while circuits particularly suited for the MG. 4 embodiment are discussed at pages 8-21 through 8-25 and 8-63.

As will be obvious to those skilled in the art, the flux distribution through the outer legs of the transformer core it may be varied by varying the resistance of element 32. Restated, the distribution of the flux generated by current flow in the primary winding i2 is effected by the load current drawn from each of the secondary windings and the load current drawn from the winding M will, as will be obvious from FIG. 2, be controlled by varying the resistance of the element 32. Since the voltage induced in the two secondary winding systems is commensurate with flux distribution in the transformer core legs, the load voltage will accordingly also be a function of the flux distribution. By proper selection of the turns ratios of the several secondary windings, the desired load voltage may be made equal to the voltage induced in series connected windings lid, l6 and 18 at the nominal source voltage level. At this time there will be maximum power dissipated in the element 32, and the voltage induced in the winding 20 will be less than that induced in series connected windings l4, lid and 253. it is to be noted that load current will nevertheless be supplied by the winding 2% under the above-described conditions and thus, since the series connected resistance element will not have the entire load current flowing therethrough, the present invention offers decided economic advantages over prior art series regulators of like character.

Considering the operating extremes, that is with the source voltage at its minimum or maximum expected levels, operating under the influence of the control 3 3, the variable resistance element 32 will be adjusted to either extreme of its operating range thus presenting, in the case of minimum source voltage, essentially a short circuit and, in the case of maximum source voltage, essentially an open circuit. In the case of the open circuit, again through proper selection of the number of turns on the winding 2%), this winding 20 will supply the desired load voltage at the maximum input voltage, there being no load current drawn from the winding M at this time and virtually all flux in the transformer core being shunted through the core leg on which windings in, 18 and 2d are wound. in the case of the shorted regulator element, the load currents drawn from the secondary windings will be distributed so as to produce equal MMF drops in the secondary legs. Under these conditions, the output voltages as induced in the secondary winding systems will be equal. The abovedescribed conditions are depicted graphically in FIG. 4 wherein the power drain in accordance with the present invention is shown by the broken line whereas the power drain attributable to conventional prior art series regulator is shown by the solid line.

Turning now to a consideration of the embodiment shown in W6. 4, it is to be noted that a conventional switching regulator achieves a constant output voltage level by varying the duty cycle of the switching element thereby coupling the source to the load with infinite or zero attenuation. in accordance with the present invention, the embodiment of FIG. 3 achieves coupling of the unregulated source to the load with a nominal transfer function; the regulation system modifying the transfer function in accordance with the source voltage. It is to be noted that the embodiment of FIG. 4 differs from that of FIG. 2 principally in that the regulating element, a switch and its control circuitry 32, does not have an intermediate position. Thus, the series regulator element of the H6. 4 em bodiment has only the open and short circuited conditions and operation intermediate these extremes is achieved by varying the duty cycle of the switch ill rather than by increasing the level of power dissipation in the series element. it is also to be noted that, as a result of the modification of the interconnection between the windings in the two secondary winding systems, the embodiment of FIG. 4 employs a pair of additional diodes 44 and as. Also, since there will be switching transients and ripple generated through the operation of the switch ill, albeit to a lesser degree thanin the prior art for the reasons to be described below, a filter comprising a series inductor 48 and a capacitor 50 is also employed in the FIG. 41 embodiment.

The operation of the embodiment of FIG. 4 may be understood by consideration of the application of an input voltage to the primary winding of the transformer, the primary winding 12 having been omitted from FIG. t in the interest of clarity, from an unregulated square wave source. With the switch 40 in the open condition, no-load current will be drawn through secondary windings 116 and lb and transformer core flux distribution will be such that equal voltages are induced in the windings l4 and Zll. These equal voltages may be considered to be the desired load voltage at the maximum level of the square wave input. At the other extreme, with the switch 40 closed and load current being drawn through the windings l6 and 18, the core flux distribution will be such that the voltage induced in the winding 29 will be equal to the combined voltages induced in series connected windings la, 16 and lb. This condition is commensurate with the minimum expected input voltage level and results in the same output voltage as achieved with maximum input voltage and the switch til) opened.

At intermediate levels of the source voltage, the switch 469 will be operated during each cycle of the source voltage to, in effect, add a synchronized square wave pulse of varying duration, the pulse width with nominal input voltage being one-half of the width of the input square wave, to the voltages induced in the windings M and Zil. Due to the presence of the diodes 22, 2 5, 26, 2b, 44 and as, a DC voltage with a ripple as shown in FlG. 5 will be applied at the input to the series inductor 45. The load voltage will, accordingly, be the average of the signal as shown in FIG. 5. It is especially to be noted that the conventional prior art switching regulator produces a much higher level of ripple since it causes the transformer output voltage to vary from zero to maximum rather than over the limited range of the hybrid switching regulator of the present invention. it is also to be noted that, since the input to the filter comprised of the inductor 4t; and capacitor 50 will essentially be DC at both extremes of the source voltage magnitude range and will not decrease to zero at any point, filter requirements are simplified and a highly efficient regulator device results. In this regard, it is to be noted that the L-C filter shown in PEG. 3 is intended as an example only.

While a preferred embodiment has been shown and described, various modifications and substitutions may be added thereto without departing from the spirit and scope of the present invention. For example, the same magnetic circuit could be used as an AC power controller, using a variable DC load, drawing current from a rectified output, to modulate the level of an AC output. Such a device would find application as an alternative to the conventional variable autotransformer (VARIAC) in applications where its limitations are significant disadvantages.

iclaim:

l. A voltage regulation apparatus comprising:

transformer core means, said transformer core means comprising a three-leg, two-window transformer core and including at least two parallel magnetic circuits;

an input winding coupled to said core means and adapted to be connected across an unregulated source of alternating current, said input winding comprising a primary winding wound on a first leg of said core;

a plurality of output windings, said output windings being coupled to preselected of said magnetic circuits whereby voltages may be inducted therein;

a fourth secondary winding wound on the third leg of said core.

2. The apparatus of claim ll wherein said flux distribution control means comprises means connecting said first, third and fourth secondary windings in series; and variable resistance means connecting said series connected windings to said second secondary windings.

3. The apparatus of claim 2 wherein said variable resistance means comprises switch means connected between one end of said second secondary winding and one end of said series connected secondary windings. 

1. A voltage regulation apparatus comprising: transformer core means, said transformer core means comprising a three-leg, two-window transformer core and including at least two parallel magnetic circuits; an input winding coupled to said core means and adapted to be connected across an unregulated source of alternating current, said input winding comprising a primary winding wound on a first leg of said core; a plurality of output windings, said output windings being coupled to preselected of said magnetic circuits whereby voltages may be inducted therein; flux distribution control means interconnecting certain of said output windings, said control means varying the flux distribution between said parallel magnetic circuits whereby the voltages induced in said output windings will vary; means for connecting said interconnected output windings across a load, said output windings comprising a first secondary winding wound on a second leg of said core; a second secondary winding wound on the third leg of said core; a third secondary winding wound on the third leg of said core; and a fourth secondary winding wound on the third leg of said core.
 2. The apparatus of claim 1 wherein said flux distribution control means comprises means connecting said first, third and fourth secondary windings in series; and variable resistance means connecting said series connected windings to said second secondary windings.
 3. The apparatus of claim 2 wherein said variable resistance means comprises switch means connected between one end of said second secondary winding and one end of said series connected secondary windings. 